1. Field of the Invention
The present invention relates to micromechanically produced valves and especially to piezoelectrically operated microvalves.
2. Description of Prior Art
Microvalves can generally be used in the fields of pneumatics and fluidics for controlling the flow of gases and liquids, i.e. fluid flows. Such a valve can either have the function of a pilot valve or it can directly be used for controlling a volume flow or a pressure in a working piston or the like.
Piezoelectrically operated microvalves which are known at present and which are based on the inverse piezoelectric effect comprise a large piezoelectric ceramic which is fixed at one end in most cases and by means of which the fluid flow is controlled directly. Such a piezoelectrically operated silicon microvalve is described in R. Ro.beta.berg, B. Schmidt, S. Buttgenbach: "Micro Liquid Dosing System", Microsystem Technologies 2 (1995), pages 11 to 16, Springer-Verlag 1995. In such microvalves, either the piezoelectric ceramic itself can serve as a valve tappet or the valve tappet used is a tappet which is directly guided by the piezoelectric ceramic.
The microvalves described in the above publication are disadvantageous insofar as, for obtaining the deflection of the valve tappet over the valve seat which is necessary for a high flow rate, a very long piezoelectric ceramic is required, said valve tappet being also referred to as valve flap. For accommodating such a piezoelectric ceramic, it is, of course, also necessary to use a correspondingly large casing. It follows that the known piezo-operated microvalves, which are described e.g. in the above-mentioned publication, have, in comparison with their construction size, a comparatively small valve opening, i.e. nominal width.
From A. Dogan, J. F. Fernandez, J. F. Tressler, K. Uchino, R. E. Newnham: "Properties of piezoelectric actuators"; Proceedings 5th International Conference on New Actuators 1996; Bremen 26th to 28th June 1996, and J. F. Fernandez, A. Dogan, J. F. Tressler, K. Uchino, R. E. Newnham: "Tailoring performance of cymbal actuators", Proceedings 5th International Conference on New Actuators, Bremen 26th to 28th June 1996, piezoelectric actuators are known, which consist of a piezoelectric ceramic material as a drive element which is arranged between two end covers having their edges connected to the ceramic material. By means of this arrangement, a lateral movement of the piezoelectric ceramic is converted into a large axial displacement at right angles to said end covers and amplified. As has been described in the publication "Tailoring performance of cymbal actuators", metals or metal alloys, e.g. zirconium, brass, low-carbon steel, molybdenum or tungsten, are used as end covers.
U.S. Pat. No. 5529279 describes a microactuator in which a thermal actuator is provided for driving a tappet, which is formed in a first substrate and which is supported in a diaphragm-like manner, for leaving an opening open and for closing it. A second substrate is connected to the first substrate and to a carrier in such a way that the tappet closes an opening which extends through said second substrate and which is in In the Abstract of JP-A-0715 8757, a microvalve is described in which a carrier plate having a passage opening is provided, a silicon diaphragm with a tappet-like portion of increased thickness being connected to said carrier plate for leaving said passage opening open or for closing it. The diaphragm is driven by a piezocomponent arranged on said diaphragm.
DE-A-4417251 describes a microvalve in which one or a plurality of passage openings in a carrier component are adapted to be closed by a movement of a closure member which is connected to said carrier component via elastic connection elements, said movement taking place at right angles to said carrier component as well as parallel thereto.
It is the object of the present invention to provide a piezoelectrically operated microvalve, the construction size of which is substantially smaller than that of known piezoelectrically operated microvalves and which, in addition, can be operated by smaller operating forces.
This object is achieved by a microvalve according to claim 1.
The present invention provides a microvalve comprising a micromechanically structured chip defining a valve seat with a flow opening therethrough, an elastic suspension device and an edge region. A valve plate is provided, which is defined by a piezoelectric actuator and which is connected to the edge region of the micromechanically structured chip, the longitudinal dimensions of said piezoelectric actuator being adapted to be changed by the application of an electric voltage. A decrease in the longitudinal dimensions of the piezoelectric actuator caused by the application of an electric voltage to said piezoelectric actuator is, due to the connection of said piezoelectric actuator with the edge region of the micromechanically structured chip and by means of the suspension device, mechanically converted into a movement of the valve plate relative to the valve seat essentially at right angles to the longitudinal direction, whereby the valve plate will open or close the flow opening in the valve seat.
The present invention is so conceived that a flow opening is provided within the valve seat which is implemented as a diaphragm portion of increased thickness, whereby the non-pressure-compensated area enclosed by the valve seat can be reduced and the force applied by the piezoactuator can be converted into an increased deflection and, consequently, into a higher flow rate through the valve.
By means of the microvalve according to the present invention, the construction size of piezoelectrically operated valves can substantially be reduced on the basis of a mechanical translation between a tappet and a piezoelectric actuator, said mechanical translation being provided by the suspension device of the tappet. By means of the lever translation, a comparatively small lateral shrinkage, i.e. a change in the dimensions of the piezoelectric ceramic in the longitudinal direction, is converted into a comparatively high vertical deflection of the valve tappet over the valve seat, i.e. a high deflection at right angles to the longitudinal dimensions of the piezoelectric ceramic. This permits large opening widths of the valve to be realized on a small area. In contrast to the hitherto known embodiments, the valves which will be described hereinbelow can, moreover, be mounted making use of a full-wafer connection technique which is generally used in the field of semiconductor technology. This means that a large number of identical components can be produced side by side ceramic. This permits large opening widths of the valve to be realized on a small area. In contrast to the hitherto known embodiments, the valves which will be described hereinbelow can, moreover, be mounted making use of a full-wafer connection technique which is generally used in the field of semiconductor technology. This means that a large number of identical components can be produced side by side on a substrate at the same time. The individual valves are then produced by dicing at the end of the manufacturing process. The use of this so-called batch process will increase the reproducability of the component specifications. By means of this kind of production it is possible to save costs, since the structures can be produced simultaneously, and to simplify production because the function can already be tested in the composite wafer structure.
The construction size of piezoelectrically operated microvalves having a structural design according to the present invention can be reduced drastically in comparison with known microvalves, the flow rate remaining, however, the same. This permits a higher packing density, e.g. in the case of so-called valve islands, so that e.g. pneumatically controlled machines can be reduced in size or actually be realized. Especially the use of microvalves in the field of motor vehicles is closely coupled with the construction size and the resultant weight of the microvalves. In addition, higher flow rates can be achieved when the hitherto used construction size is maintained. It follows that faster switching times, e.g. of working pistons, can be achieved. Due to the reduced construction size required for a given flow rate, the costs for the casing will be reduced as well.